In recent years, there is an increasingly compelling feeling that intracellular calcium may play an important role in the regulation of liver carbohydrate metabolism by insulin, glucagon and the catecholamines. The importance of the cyclic nucleotides in mediating hormone action on liver function is well recognized, but it is increasingly evident that other intracellular messengers, perhaps calcium, may be involved. The case for calcium playing a determinant role is still purely circumstantial. This research proposal plans to investigate rat liver cell calcium metabolism in vivo and in vitro, in diabetes and in fasting, and the influence of insulin, glucagon and the catecholamines upon it. At the same time, liver cyclic nucleotide concentrations (cyclic AMP and cyclic GMP), intracellular pH and when appropriate, liver enzymatic activity (phosphorylase a, glycogen synthetase) or gluconeogenesis will be determined in an attempt to correlate liver function, cyclic nucleotide levels and cellular calcium. Liver cell calcium metabolism will be studied in isolated rat hepatocytes or in rat liver slices 1) by chemical measurements of whole cells or tissue 40Ca concentration 2) by chemical determination of 40Ca in subcellular components, such as mitochondria and microsomes 3) by kinetic analysis of 45Ca uptake curves 4) by kinetic analyses of 45Ca desaturation curves 5) by computer analysis of fractional 45Ca efflux profiles produced by various hormones. Intracellular pH will be monitored by the weak acid distribution method. Cyclic nucleotides concentration, adenylate and guanylate cyclase activities will also be determined. Chronic and acute diabetes will be produced with alloxan and anti-insulin serum. The effects of insulin, glucagon, and catecholamines will be studied both in vivo and in vitro.